The response of the Southern Benguela coastal upwelling to variable wind forcing

A regional high resolution hydrodynamic model is used to investigate the response to atmospheric forcing of the Southern Benguela coastal region (southeast Atlantic), including the west coast upwelling area and western Agulhas Bank. When forced by climatological winds, the model gives a realistic portrayal of the regional circulation and of the coastal oceanographic structures, including a highly energetic mesoscale activity. The role of the regional wind stress in participating to the development of inter-annual sea surface temperature (SST) anomalies is investigated by forcing the model with realistic wind extracted from ERS1/2 weekly wind database. Comparisons between simulations that differ only in the amount of inter-monthly and inter-annual variability kept on the wind forcing show a surprising contrast between the response of the Agulhas bank and the West Coast upwelling region. Up to 90% of the interannual SST variability over the Agulhas Bank can be attributed to the wind stress. Over the western continental shelf, wind contribution to interannual SST variability ranges between 30 and 70%, and a large portion of the west coast region appears to be affected by surface mesoscale currents, no matter the existence of obvious upwelling or downwelling signals in the surface wind. The fair correlation obtained at several locations between model SST and concomitant observations confirms the interest of a regional numerical tool to study and account for anomalous events observed in the Benguela system.